This invention relates generally to fuels cells, and more particularly to proton exchange membrane fuel cells having improved gas diffusion layers.
Historically, most developments in fuel cell technology involved applications supported by the government, such as the United States National Aeronautics and Space Administration (NASA), or applications related to electrical utility plants. However, recent developments in materials of construction and processing techniques have brought fuel cell developments closer to significant commercial application.
An important advantage of fuels cells is their 60–70% efficiency in converting stored chemical energy to electricity, with even higher efficiencies being theoretically possible. In addition, fuel cells produce virtually no pollution. These advantages make fuel cells particularly suitable for vehicle propulsion applications and replacement of internal combustion engines, which operate at less than 30% efficiency and which can produce undesirable emissions.
Generally, fuel cells operate by oxidizing a compound or molecule (that is, chemically combining with oxygen) to release electricity and thermal energy. Currently, there are a variety of fuel cell operating designs that utilize many different fuel and oxidant combinations. The most common fuel/oxidant combination is hydrogen and oxygen. In a typical fuel cell, hydrogen is consumed by reacting the hydrogen with oxygen (usually from air) to produce water, electrical energy, and heat. This is accomplished by feeding the hydrogen over a first electrode (anode), and feeding the oxygen over a second electrode (cathode). The two electrodes are separated by an electrolyte, which is a material that allows charged molecules or “ions” to move through it. Several different types of electrolytes can be used, including acid-type, alkaline-type, molten-carbonate-type, and solid-oxide-type. Proton exchange membrane (PEM) electrolytes (also known as solid polymer electrolytes) are of the acid-type, and they potentially have high-power and high-voltage, making them desirable for fuel vehicle applications.
In order for fuel cells to operate efficiently, it is often important for the system to be hydrated. The water required to hydrate the system may be carried in the anode and/or the cathode gas streams. Water is often available from the electrochemical reaction occurring in the fuel cell, and may be collected to be used in external humidification systems (i.e., external to the fuel cell stack) to hydrate the anode and cathode streams. However, these external humidification systems are often complex and reduce overall system efficiency.
Therefore, there is a need for a less complex fuel cell system which prevents the proton exchange membrane from drying out during operation.